London: The London Games finally got a fleeting glimpse of the world's fastest man Usain Bolt on Saturday as the Olympic 100 metres champion enjoyed nothing more than a light canter after a sloppy start to safely reach the semi-finals.

The leading protagonists for Sunday's blue riband showdown, including world champion Yohan Blake, Jamaican compatriot Asafa Powell and Americans Justin Gatlin and Tyson Gay all enjoyed a comfortable passage.

On a track described by the stadium's PA as a "magic carpet", Bolt stumbled slightly at the start but still barely broke sweat on a sunny morning for the second day of track and field action.

"I made a bad step. I stumbled a bit. I'm glad it happened now," the Jamaican said after easing home in 10.09 seconds in the fourth heat.

Bolt shared the stage with South Africa's "Blade Runner", Oscar Pistorius, who became the first double amputee to compete on the track at an Olympic Games.

Pistorius, who wears carbon fibre prosthetic blades after being born without a fibula in both legs, qualified for the 400m semi-finals to huge cheers with a season's best of 45.44 seconds.

British hopes of a gold-tinged evening later on Saturday grew when Jessica Ennis stretched her lead in the heptathlon with just the 800 metres remaining.

Bolt entered the arena well wrapped up in beanie hat and hooded top as he went through some stretching routines, half-heartedly acknowledging the crowd before touching knuckles with the official behind his starting block.

The Jamaican, disqualified for false-starting in the world final in Daegu, South Korea, last year and entering these Games with doubts over his fitness, said he was "running well" and his training had been "great".

The semi-finals and final are on Sunday.

Blake looked in good form by clocking 10.0, as did 2004 Olympic champion Gatlin (9.97) who was one of two runners to dip under 10 seconds. American Ryan Bailey signalled that he will be in the medals shake-up by dashing to 9.88, the fastest of the day.

Former world champion Kim Collins was a surprise absentee from the heats with local media reporting that the St Kitts &amp; Nevis runner had fallen out with his country's officials over a visit from his wife.

The 2003 world champion hinted as much on Saturday when he tweeted: "Even men in prison get their wives to visit. 6 athletes and 9 officials. That ain't enough to make some people happy. Omg."

Poster Girl

Britain's track poster girl Ennis remained on course to be crowned Olympic heptathlon champion after consolidating her overnight lead following the morning's long jump and javelin.

Ennis, who missed the Beijing Games through injury, holds a 188-point lead over Lithuanian Austra Skujyte and has the gold medal firmly in sight.

While Ennis appears inspired by the fervent home support, Pistorius revelled in the roars of another 80,000 crowd.

"I was so nervous this morning," the 25-year-old said.

"Thanks to everyone for showing their support. I didn't know whether to cry. I had a mixture of emotions. It was the most amazing experience... I saw the South African flag. I've run so much in the UK it feels like my second home."

World 400 champion Kirani James breezed through but Olympic champion LaShawn Merritt was the biggest casualty of morning qualifying with the American, who had been suffering from a hamstring injury coming into the Games, pulling up in his heat.

Merritt, who appeared on the track with a heavily strapped left thigh, served a 21-month suspension after a positive doping test for using of an over-the-counter male enhancement product in 2010 which contained a banned substance.

Six golds are up for grabs on Saturday, beginning with the men's 20km race walk (1600) which starts and ends on The Mall in central London.

The women's 100 metres final (2055), in which Jamaica will look to repeat their podium clean sweep in Beijing, and the men's 10,000 metres final (2015), with Mo Farah carrying home hopes on his slender shoulders, provide the highlights of the evening session.

As well as the conclusion of the heptathlon, the men's long jump (1855) and women's discus finals (1830) will also be decided.